1. Field of the Invention
This invention relates to a vibration-isolating device mainly used for automobile engine mounts, suspension bushings, etc.
2. Description of the Related Art
Bush type of vibration isolators for use in vehicle engine mounts, suspension bushings, etc. have heretofore been known, in which an inner cylindrical fitting and an outer cylindrical fitting are connected by a rubber elastomer interposed between them. Usually the inner cylindrical fitting is attached, through a shaft member inserted therein, to the one support member whereas the outer cylindrical fitting is press fitted in the other support member such as bracket, etc., whereby the vibration isolator is fixed. These support members are fitted on the vibration source side, e.g., power unit such as engine and on the support side such as vehicle body.
The vibration isolators of this kind is, as shown in FIG. 10, typically constructed so that an inner cylindrical fitting 51 and an outer cylindrical fitting 52 are connected by a rubber elastomer 53 interposed between both fittings 51, 52, in the rubber elastomer 53 there are defined hollow spaces 54, 55 having circumferentially a required width so as to oppose to each other above and below the inner cylindrical fitting 51, and the rubber elastomer 53 between the hollow spaces 54, 55 supports at its lateral portions 53a, 53b the inner cylindrical fitting 51 relative to the outer cylindrical fitting 52.
The design of this vibration isolator is based on that for instance, where it is used to restrain the fore-and-aft vibration of the power unit, with its axial direction (X-direction) oriented in a lateral direction to the vehicle, the spring in the up-and-down direction (Z-direction) to the fore-and-aft direction (Y-direction), which is the lateral direction square to the axial direction, is soft and flexible because of the upper and lower hollow spaces 54, 55, whereby predetermined vibration-isolating characteristics required for the vertical vibration are available.
In the preceding example of vibration isolator, in particular with such a construction that, in the state of use, supports the inner cylindrical fitting 51 at lateral portions 54, 55 of the rubber elastomer 53, the dynamic spring rate in the fore-and-aft direction is high as compared to the vertical (up-and-down) direction and consequently, the vibration-isolating performance to the vibration in the fore-and-aft direction is too inferior and the volumes of the lateral portions 53a, 53b are too larger to be satisfactory. That is, the input of vibration load in the vertical direction causes high compression stress and tensile stress to the lateral portions 53a, 53b. As a result, heat is evolved at the lateral portions and it is likely that breakdown or cracks develop, which deteriorates the durability. Therefore it is desired to lower the dynamic spring rate in the fore-and-aft direction.
For instance, if the form of the hollow space and the configuration of the aforementioned lateral portions are altered in order to lower the dynamic spring rate of the lateral portions in the fore-and-aft direction, which is the lateral direction square to the axis, the spring in the up-and-down direction and vibration isolating characteristics or other characteristics are affected thereby. Consequently, the required performance cannot be achieved, the durability is deteriorated, and besides, the tuning of rigidity becomes difficult.
The present invention has been made in view of the problems described above, and it is a principal object of the invention to provide a vibration-isolating device capable of reducing the dynamic spring rate mainly in the lateral direction square to the axial direction, namely the fore-and-aft direction and tuning easily the rigidity without altering the vibration-isolating characteristics and without deteriorating the durability.
This invention relates to a vibration isolating device which comprises an inner cylindrical fitting, an outer cylindrical fitting disposed outside to surround the inner cylindrical fitting, and a rubber elastomer interposed between the inner and outer cylindrical fittings, the rubber elastomer having therein circumferentially hollow spaces defined above and below the inner cylindrical fitting, the hollow spaces extending in a larger width, in the cross-section square to the axial direction, than the outside diameter of the inner cylindrical fitting, the rubber elastomer between the upper and lower hollow spaces constituting lateral portions, the lateral portions serving to support the inner cylindrical fitting to the outer cylindrical fitting; and which is characterized in that the lateral portions of the rubber elastomer are defined axially with small vacancies spaced apart inboard of the outer cylindrical fitting.
The vibration isolation device of this invention is thus provided axially with small vacancies at the lateral sides of the rubber elastomer, thereby making it possible to reduce the dynamic spring rate in the lateral direction square to the axial direction without altering the form of the hollow spaces and the contour of lateral portions and without affecting the dynamic spring rate and vibration isolating characteristics in the up-and-down direction. On account of the advantage, for example, where it is used with the axial direction oriented in the lateral direction to the vehicle, vibration-isolating characteristics in the fore-and-aft direction can be improved.
The small vacancies are provided at a distant position from the outer cylindrical fitting and as such it is possible to inhibit the evolution of heat in the rubber elastomer, which is ascribed to the vibration in the lateral direction square to the axial direction, by heat dissipation effect due to the small vacancies, thus preventing the deterioration in durability.
In particular, where the small vacancies are provided in the vicinity of the midpoint between the inner and outer cylindrical fittings in the lateral portions of the rubber elastomer, evolution of heat can be inhibited effectively because the vicinity of the midpoint is large in compression and tensile movements owing to the input of vibrational load in the lateral direction square to the axial direction and accordingly, is most liable to evolve heat.
In the preceding vibration isolation device, the small vacancies are either non-through-holes or through-holes. In either case, tuning of the rigidity is easy and feasible as compared with the case where no small vacancies are provided.
In particular, where the small vacancies are not through-holes, the rigidity is set higher than the case of through-holes owing to the existence of the non-pierced portion, and the tuning of rigidity becomes easy by varying and adapting the diameter of the non-through-holes, the depth of the holes, and accordingly, the wall thickness of the non-pierced portion. The design freedom is thus expanded.
In accordance with this invention it is also possible to provide each of the lateral portions of the rubber elastomer with a plurality of small vacancies. In this case, it is likewise possible to restrain further effectively the heat evolution at the lateral portions owing to heat dissipation effect of the small vacancies and to facilitate the tuning of rigidity.
In the preceding vibration-isolating device, the inner cylindrical fitting is preferred to be disposed eccentric upwardly to the outer cylindrical fitting under non-loading condition so as to be supported nearly concentrically under a predetermined load, whereby its vibration-isolating characteristics are stabilized.
Alternatively it is possible to construct so that the outer cylindrical fitting has a laterally long ellipsoidal shape in cross-section and the lateral portions of the rubber elastomer support the inner cylindrical fitting from both lateral sides in cross-section of the outer cylindrical fitting. By doing so, in case where the axial direction of the vibration-isolating device is oriented in the lateral direction, a long ellipsoidal shape in the fore-and-aft direction in cross-section is resulted, and as a result, the inner cylindrical fitting can be supported by a sufficient volume of the rubber elastomer from both sides in the fore-and-aft direction, stabilizing further the vibration-isolating characteristics.